Conversion of hydrocarbons



Sept- 26, 1944- H. DIMMIG v 2,358,912

CONVERSION 0F HYDROC-ARBONS Filed'May 24, 1940 H ls ATTORNEY 'ofconversion.

Patented Sept. 26, 1944 2,358,912 y l y CONVERSION oF HrnRocAmsoNs Howard Dimmig, Katonah, N. `Y., assigner to Gasoline Products Company, Inc., Jersey. City, N. J., a corporation of Delaware Application May 24, 1940, Serial No. 336,924

efclaims. (cl. 19e- 50) This invention relates to the Vconversion of hydrocarbons and has particularV reference to certain improvements associated with the cooling or quenching of the products of conversion.

In the cracking or conversion of light hydrocarbons, such as in the pyrolysis or polymerization of normally gaseous hydrocarbons and in the cracking of light oil stocks as in the reforming of naphtha or gasoline stocks, the products of conversion leaving the reaction zone consist of a small amount of heavy tarry matter,y varying amounts of gasoline and normally gaseous hydrocarbons and relatively small proportions of constituents of boiling range intermediate the gasoy line and the tar. Because of its composition the mixture of products leaving the reaction zone is no doubt ordinarily in a single phase, i. e., in a gaseous or vapor phase at the temperatures and pressures usually existing in the transferv line from the reaction Zone. Any material reduction in the temperature of the mixture of products leaving the reaction Zone will result in phase separation and the material rst separated out as a result ofthe cooling is avery heavy tar of high viscosity and of lrelatively poor thermal stability. The heavy material thus separated tends to be deposited on the walls of the transfer line and to decompose causing carbon or coke deposition which sooner or later necessitates an interruption of the operation.l I

A common method of procedure is to introduce a cooling or quenching liquid into the transfer line mixture, at temperatures very materially lower than that of the mixture with Vthe object in view of retarding or preventing further cracking and avoiding any unduecoke formationlin the transfer line and heat exchangers, as well as in the subsequent fractionation of the products I have found that when using a quenching medium in this manner there is a tendency toward the cooling of the transfer line and in certain cases that the thermal conduction of the metal tends to cool a material portion of the transfer line stream at some distance upstream from the quench point and as aresult phase separation occurs which results in the deposition of heavy tarry material in the transfer line,lev'entually resulting in coke formation so that transferline stoppageoccurs upstream from the quench point.

In accordance with my invention these difficulties are overcome by introducing a liquid solvent or oil into the transfer line at a temperature approximating that of the products of con,- version therein. The introduction of the oil tends gas `separator I8 having a gas outlet I9.

to raise the dew point of the transfer line mixture and so functions that when, and as,-any phase separation occurs the rst condensate has a much lowerviscosity (better fluidity) and a much better thermal stability than the heavy tar which separates normally without the introduction of the hot quench, with the result that the condensed liquid may be carried along in the transfer line stream without deposition on the walls of the transfer line and without decompo sition into coke.-

In practicing the invention hydrocarbon oil higher boiling than gasoline is heated to a temperature approximating that' of the stream of cracked products which it is desired to cool or quench and the preheated oil is introduced into the transfer line. The resulting mixture is then subjected to cooling by reduction in pressure or by being contacted with Ya cooling medium or by both the introduction of a cooling medium and reduction in pressure. 1t is desirable to employ as the heatedmedium which is introduced into the stream of products of conversion a relatively refractory stock such as a stock derived fromV a previous cracking or conversion operation so that there will be a minimum extent of cracking of the introduced stock. Y It is also desirable to employ a stock of intermediate boiling range such as gas oil. Ordinarily the quantity of hot quench oil required Will be of the order of 10%,-30% of the products (liquid volume) leaving the reaction zone.

For the purpose of more fully disclosing the invention reference is now had to the accompanying drawing which is a flow diagram illustrating a particular example of the invention in which it is applied in a gas reversion process.

In the drawing the heating coil I0 is adapted to be heated to a desired cracking or conversion temperature by means of the furnace II and oil stock for conversion isintroduced by pump l2 to the heatingfcoil I0. The products of conversion pass through a transfer line I3 to a separating and fractionating tower I4. A pressure reduction Vvalve I5 is ordinarily disposed in the transfer line. In the tower I4 the products of conversion are separated into vapors and residue and the vapors are subjected to fractionation to form reflux condensate which may be collected in a tray I6. Uncondensed vapors and gases pass overhead from thetower to a condenser Il and the gasoline or motor fuel distillate of'desired boiling range is collected in a receiving drum or The distillate is directed by a pump 20 to a rectifying tower or stabilizer 2| wherein it is subjected to rectification to produce a gasoline or motor fuel product of desired vapor tension which may be removed through line 22. Uncondensed gases are conducted by a line 23 to a pump or compressor 24 by which the normally gaseous constituents are directed to the conversion coil I for polyrnerizing or reversion reactions in Contact with the liquid oil stock undergoing reaction therein.

An extraneous oil is drawn from a suitable source through a line 25 and conducted by a pump 26 through a line 2'I to a heating coil 28 mounted in a furnace 29 in which the oil is adapted to be heated to approximately the terri'-V perature of the oil stream which enters theV transfer line I3 from the conversion coil I0.

in the tower I4. A bottom temperature of about 700 F. is maintained in the tower I4,

In practicing the invention the same stock may be used in both the hot solvent and the cooling operations, as in the preceding example, or different stocks may be employed,

Although a preferred embodiment of the invention has been described herein, it will be understood that various `changes and modifications may be made therein, while securing to a greater or less extent some or all of the benefits of the invention, without departing from the spirit and scope thereof.

-The

heated oil passes from the heater 28 through line 30 to the transfer line I3.

with a branch line 3I so that reflux condensateV from tray I6 may also be directed through the heating coil 28. Y

A line 32 is provided for introducing a cooling medium drawn from any suitable source to the transfer line` I3 at a point downstream from the juncture of the transfer line with line 30. Itis sometimes advantageous to` connect the line 32 with the line I3 directly at the valve I5. Line 32 is shown as extending to the Vline 2'I 'so Vthat a portion of the extraneous stock introduced through line or a portion of the mixture `of the extraneous stock and cycle stock from tower I4 may be employed as the cooling` medium.. A

by-pass line 33 is shown having a'pump 3lIbyk which that portion of the cycle stock desired for cooling may be directed througha cooling `coil 35 and passed thence through line 32 to the transfer line I3.

In an example of the invention a naphtha stock is directed by the pump I2 to the reaction coil IIJ and cycle gases consisting predominantly of C3 and C4 hydrocarbons which are recovered fromv the stabilizer 2I are mixed with the naphtha for polymerizing and reversion reactions in the coil I0. The mixture of naphtha and cycle gases is subjected to Va temperature, such as 1000 F.-1050 F. under high pressure of the order of 600 or 1000 pounds or even up to 1600 pounds, to effect reforming o-f gasoline constituents and reversion of gaseous hydrocarbons and the products of conversion are passed into the transfer line I3. An extraneous stock derivedfroml a previous cracking operation and having the fol-lowing inspection is used for both the heated solvent and for the quenching or cooling stock:

Gravity A, P. I 12.0 I. B, P F 600 50% 675 E. P 750 Initially in the run the extraneous stock is employed in the hot solvent andcooling operations but after operating conditionsare establis-hed condensate from tower I 4 is* added to the `extraneous stock. The hot quench stock is quickly Iheated to about 1,000 FQin the heating coil 28 Line 25 is provided f l I claim:

1. In the conversion of relatively light hydrocarbons of the nature of normally gaseous hydrocarbons andgasoline hydrocarbons wherein the hydrocarbons are heated to a cracking temperature in a heating zone and subjected to convalve I5 tomaintain apressure-of about 200 lbs. 75

version to produce a resultant vaporous mixture of reaction .products composed of a relatively small proportion of potential, tarry or residual constituents, a relatively large proportion of gasoline hydrocarbons and normally gaseous hydrocarbons and a relatively small proportion of intermediate constitutents and wherein the vaporous mixture is passed in a continuous stream from the heating Zone toa separating zone, the process that comprises introducing into said continuous stream flowing from the heating zone to the separating zone, prior to any substantial cooling thereof, a heated oil consisting essentiallyjfof lconstituents boiling within a range of 600 Fl to 750 F. and in sufficient quantity to raise the dew point` of the mixture without substantially lowering the temperature thereof so that upon subsequent cooling and phase separation'said heated oil so introduced Will function to dilute the rst tarry constituents condensed out and lowerA the viscosity thereof, thereafter introducing into the stream a relatively cool oil to lowerthe temperature thereof and separating the cooled products into vapors and residue.

2 VIn the conversion of relatively light hydrocarbons of Vthe nature of normally gaseous hydrocarbons and gasolineY hydrocarbons wherein the hydrocarbons are heated to a cracking temperature'in a heating zone and subjected to conversion to produce a resultant vaporous mixture of reaction products composed of a relatively small proportion of potential tarry or residual constituents, a relatively large proportion of gasoline hydrocarbons and normally gaseous hydrocarbons and a relatively small proportion of intermediate constituents and wherein the vaporous mixture is passed in a continuous stream from the heating zone to a separating zone, the process that comprises introducing into said continous stream flowing from the heating Zone to the separating'zone, prior to any substantial coolingV thereof, a heated oil stock comprising essentially constituents boiling within a range of 600 ZE. to 750 F. in a quantity of the order of 10% Vto 30% of the liquid volume of the products flowing in said stream to thereby raise the dew pointY of the mixture without substantially lowering the temperature thereof so that upon subsequent cooling andphase separationvsaid oil stock so introduced will function to dilute the first tarry constituents condensed out and lower the viscosity thereof and thereafter subjecting the mixture having the increased dew pointto cooling to produce phase separation.

3In the conversion of relatively light hydrocarbons of the nature of normally gaseous hydroprocess that comprises rapidly passing a ther-V mally refractory gas oil stock in a quantity of the order of 10% to 30% of the liquid volume of said stream through a heating zone wherein it is brought to a temperature approximating that of said continuous stream under conditions to prevent substantial cranking, introducing the resultant heated higher boiling stock into said continuous stream flowing from the heating zone to the separating zone, prior to any substantial cooling thereof, to thereby raise the dew point of said continuous' stream without substantially lowering the temperature thereof so that upon subsequent cooling and phase separation the oil so introduced will function to dilute the first tarry constituents condensed out and lower the viscosity thereof, thereafter introducing into the vstream a relatively cool oil to lower the temperature thereof and reducing the pressure thereon for delivery to the lower pressure separating Zone.

HOWARD DIMMIG. 

